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[求助]
蔗糖按EP检验亚硫酸盐检查问题
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蔗糖按EP7.0检验，其中亚硫酸盐一项不太明白，特请教各位： 见粗体部分，添加多少试剂？如何判断反应终点？ 方法原文如下： Sulfites: maximum 10 ppm, calculated as SO2. Determine the sulfites content by a suitable enzymatic method based on the following reactions. Sulfite is oxidised by sulfite oxidase to sulfate and hydrogen peroxide which in turn is reduced by nicotinamide-adenine dinucleotide-peroxidase in the presence of reduced nicotinamide-adenine dinucleotide (NADH). The amount of NADH oxidised is proportional to the amount of sulfite. Test solution. Dissolve 4.0 g of the substance to be examined in freshly prepared distilled water R and dilute to 10.0 mL with the same solvent. Reference solution. Dissolve 4.0 g of the substance to be examined in freshly prepared distilled water R, add 0.5 mL of sulfite standard solution (80 ppm SO2) R and dilute to 10.0 mL with freshly prepared distilled water R. Blank solution. Freshly prepared distilled water R. Separately introduce 2.0 mL each of the test solution, the reference solution and the blank in 10 mm cuvettes and add the reagents as described in the instructions in the kit for sulfite determination. Measure the absorbance (2.2.25) at the absorption maximum at about 340 nm before and at the end of the reaction time and subtract the value obtained with the blank. The absorbance difference of the test solution is not greater than half the absorbance difference of the reference solution. |
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